learning how to punch properly will make them stronger go to boxing, the tricep is where a huge amount of punching power comes from because it is responsible for extending your arm so train triceps, turn your waist into the punch this will put more power behing it

You guys are all forgetting the legs! Where do you think your power comes from when you're punching? Try hanging from a rope and punching and see how hard you can hit. In addition to building everything already said, improve your leg strength and quickness. Also, you may want to work on EXPLODING on every rep.

"If you want to be world class you must first act world class" -Travis Ortmayer

Power comes from the core. Only about 10% of the power comes from the arm, check out a site like sherdog and that will give you the answers your looking for. This is a bodybuilding site not a boxing site!

The best way to increase punch strength as a beginner is to get a heavy bag and beat it up. You will learn proper coordination to throw a punch and that is where you'll see the greatest improvement in your power.

Also big compounds will help with punch strength because they will teach your body how to work together as a whole. So things like bench press, clean and press, overhead squat and others will all increase explosiveness, thereby giving you a stronger punch.

Punching with weights in your hands may not be the best idea, especially if you arent throwing the punches at a bag. It can cause your arm to hyperextend when you stop the weight from going forward.

The best way to increase punch strength as a beginner is to get a heavy bag and beat it up. You will learn proper coordination to throw a punch and that is where you'll see the greatest improvement in your power.

That is also the best way of picking up habbits. You can have an amazingly strong punch but if you don't learn how to defend your going to get you ass kicked.
Punch through the target once your fist makes contact it should either stay the same speed or increase speed this will hurt more than a punch that hits you just fizles away.